Book excerpt: The most common image of world politics involves states negotiating, cooperating, or sometimes fighting with one another; billiard balls in motion on a global pool table. Yet working through local proxies or agents, through what Eli Berman and David A. Lake call a strategy of "indirect control," has always been a central tool of foreign policy. Understanding how countries motivate local allies to act in sometimes costly ways, and when and how that strategy succeeds, is essential to effective foreign policy in today's world. In this splendid collection, Berman and Lake apply a variant of principal-agent theory in which the alignment of interests or objectives between a powerful state and a local proxy is central. Through analysis of nine detailed cases, Proxy Wars finds that: when principals use rewards and punishments tailored to the agent's domestic politics, proxies typically comply with their wishes; when the threat to the principal or the costs to the agent increase, the principal responds with higher-powered incentives and the proxy responds with greater effort; if interests diverge too much, the principal must either take direct action or admit that indirect control is unworkable. Covering events from Denmark under the Nazis to the Korean War to contemporary Afghanistan, and much in between, the chapters in Proxy Wars engage many disciplines and will suit classes taught in political science, economics, international relations, security studies, and much more.